Recently, MIMO (multiple input multiple output) system has been in the spotlight of the broadband wireless mobile communication technology. The MIMO system means the system that raises communication efficiency of data using multiple antennas. And, the MIMO system may be implemented using such an MIMO scheme as a spatial multiplexing scheme or a spatial diversity scheme in accordance with a presence of non-presence of transmission of the same data.
The spatial multiplexing scheme means the scheme for transmitting data at high speed by transmitting different data via a plurality of transmitting antennas simultaneously without increasing a bandwidth. The spatial diversity scheme means the scheme for obtaining transmission diversity by transmitting the same data via a plurality of transmitting antennas. Space time channel coding is an example for the spatial diversity scheme.
The MIMO technique can be also categorized into an open loop scheme and a closed loop scheme according to a presence or non-presence of feedback of channel information to a transmitting side from a receiving side. The open loop scheme includes a space-time trellis code (STTC) scheme for obtaining a transmission diversity and coding gain using BLAST and space region capable of extending an information size amounting to the number of transmitting antennas in a manner that a transmitting side transmits information in parallel and that a receiving side detects a signal using ZF (zero forcing) and MMSE (minimum mean square error) scheme repeatedly. And, the closed loop scheme includes a TxAA transmit antenna array) scheme or the like.
In a wireless channel environment, a channel state changes irregularly in time and frequency domains, which is called fading effect. Therefore, in order to reconstruct data transmitted from a transmitter and to obtain a correct signal, a receiver corrects a received signal using channel information.
A wireless communication system obtains channel information in a manner of transmitting a signal known to both of a transmitter and a receiver and then using an extent of distortion of the signal transmitted on a channel. This signal is called a reference signal (or a pilot signal). And, a process for obtaining the channel information is called channel estimation. The reference signal does not include data actually and has a high output of power. In case that data is transmitted and received using multiple antennas, it may be necessary to know a channel status between each transmitting antenna and each receiving antenna. Hence, a reference signal exists for each transmitting antenna.
In a legacy LTE system, a single antenna is used for an uplink (UL) control channel transmission. In LET-A system of a next generation mobile communication system, a multi-antenna transmission scheme is introduced to enhance performance of the UL control channel. It may be difficult to apply a UL transmission channel power in a legacy LTE system to an LTE-A system that uses a plurality of antennas. However, when the number of antennas used for a control channel transmission in LTE-A system changes or a transmit diversity scheme changes, any efforts has not been made to research and develop how to determine and control a UL transmission power.